The present invention relates generally to methods of, and apparatus for accurately monitoring the amount of biocides and particular oxidants present in a given water volume. Oxidants such as sodium hypochlorite and other halogen-based compositions (including but not limited to Actibrom, BCDMH, and Stabrex) are frequently used to control the growth of microbial organisms and. other biological deposit formations in water and industrial processes. Efficient and effective use of these compositions however requires that proper concentrations be maintained. This is best achieved by use of an online system that provides real time up to date concentration information.
One on-line method of monitoring the concentrations in water involves determining the amount of total halogen and free halogen residuals. This can be accomplished by a number of commercially available devices using various techniques. The HACH CL17 measures free and total chlorine using colorimetric method and N,N-diethyl-p-phenylenediamine (DPD) indicator reagent. Unfortunately, the use of such colorimetric and indicator reagents is limited to water systems with low solids and with turbidity values below 5 nephelometric turbidity units (NTU). Paper process water typically has a solids content ranging from 0.1 to 0.5% even in the most clarified parts of the process, which greatly exceeds the limitations of available technology.
Another method is Oxidation-Reduction Potential (ORP). ORP however only gives an indirect measurement of oxidant concentration. Also because ORP is affected by factors other than just halogen concentration. under certain circumstances, and in particular in highly turbid environments it is inaccurate.
Yet another method is Amperometric measurements. Amperometric measurements use a conductive element sensor (typically having a copper and platinum or gold electrode). A small amount of potential is applied to the sensor electrodes. An electric charge is then generated by the chemical reduction of the oxidant. The resulting charge is in direct linear proportion to the amount of residual halogen present in the sample. Amperometric measurements however require membrane caps, which rapidly become fouled when continuously used in many industrial processes. As a result, Amperometric measurements are only of limited practical use.
It is therefore useful and desirable to provide methods and apparatus to better detect the concentration of oxidants in water samples. The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “Prior Art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR §1.56(a) exists.